1/ I'm not sure what JSB is, so I guess my answer is "No".
Construct exports to HTML5/JS. The other exports are wrappers and adaptation to the specified platforms.
Manual page on exporting games from Construct
2/ Performance are pretty good, as long as you respect the performance tips and memory usage tips.
Make sure your mobile phone supports the minimum system requirements : construct.net/en/make-games/manuals/construct-3/getting-started/system-requirements
Our team is keen on bringing the more stability and performances as possible.
Consider possibly making a bug report for your FPS issue on our bug report platform
Please note that using the debugger may have an impact on the performances.
To best monitor a game aimed at being published on mobile, you might need to export an actual debug version of your game and monitor from your computer.
Topic on the subject of debugging a debug APK on Android for example
3/ Yes.
Dedicated manual part about Scripting
And you can also find examples in the start page of Construct 3, category "Scripting"